Petroleum products, such as fuels and lubricants, are characterized in part by the physical changes they exhibit at certain temperatures. Indeed, these temperature related changes are commonly used as specifications for fuels and lubricants. One such change is the hydrocarbon's cloud point. As is well known, the cloud point is the temperature at which dissolved solids in a fuel or lubricant, such as paraffin wax, begins to form and separate from the hydrocarbon. Another important property of fuels and lubricants is their pour point. The pour point is the lowest temperature at which the petroleum product will flow. Both cloud point and pour point are properties that can be critical to the performance of the fuel or lubricant.
Standard tests have been developed by the American Society for Testing Materials (ASTM) to determine cloud and pour point temperatures such as ASTM D2300-91 and ASTM D97-87. Both these tests require hands-on manipulation of petroleum product samples to determine the cloud and pour point temperatures.
Somewhat more sophisticated devices have been developed for measuring the cloud point of a petroleum product which are largely based on some optical measurement of an appropriately cooled sample.
Another physical property of petroleum products, which is important at least from an aesthetic and economic aspect, is their appearance. Products that are clear and bright are more highly valued than those that are hazy. Thus, in preparing a petroleum product such as a finished heavy lubricant base stock, a dewaxed oil will be subjected to a dehazing step to improve its appearance. As is known, dehazing is typically achieved by either catalytic or absorptive methods or by filtration to remove those constituents that result in haziness. Experience has shown, however, that a lubricant base stock may be produced that has a satisfactory cloud and pour point and that is clear and bright right after it is cooled to room temperature but may upon storage develop a haze. This phenomenon is referred to herein as delayed onset haze formation. Because delayed onset haze often does not manifest itself for an extended period of time, often as long as six months, it is difficult to know whether the lubricant will develop a haze during its expected shelf life. The temperature at which haze will not exist in the petroleum product is referred to herein as the haze disappearance temperature. Clearly it is highly desirable to be able to monitor and control the lubricant forming process to assure that the finished lubricant base stock has an acceptable delayed onset haze property or haze disappearance temperature.
While light scattering techniques have been used to measure various lubricant properties such as cloud and pour point, the use of such techniques to monitor and control delayed onset haze formation or haze disappearance temperature has not heretofore been explored or achieved.
Therefore, a need exists for an apparatus and method for rapidly determining whether a petroleum product will manifest delayed onset haze formation and the temperature at which haze will not exist. A need also exists for an apparatus which can be utilized on line and in real time with a petroleum process to control the process to produce products having predetermined haze properties.
The present invention is directed toward meeting the foregoing needs as well as other needs as embodied and broadly described herein.